Local radiotherapy was successful in decreasing refractory bone pain in mastocytosis patients with significant bone erosion. This severe intractable bone pain is seen in patients with aggressive disease and is usually treated unsuccessfully with narcotic analgesics. Studies are underway to assess cytokine profiles in mastocytosis patients. Suction blisters are raised over urticaria pigmentosa lesions which contain collections of mast cells. Blister fluid is assayed for cytokines appearing in blister fluid over several hours. A new improved serum assay for mast cell-derived tryptase may result in improved diagnosis for systemic mast cell disorders. Significant liver disease is seen in association with aggressive mast cell disease (Categories II and III). Pathology includes mast cell infiltrates, inflammation around the portal triads, and fibrosis. A retrospective review of the bone scans of 75 mastocytosis patients has demonstrated that bone scanning provides an efficient, noninvasive method of assessing and following active bone and bone marrow involvement. As the disease progresses, abnormalities on bone scan become increasingly diffuse. Progression of disease on serial bone scans occurs in patients more likely to have a malignant course.